The Great God Pan is a novella written by Arthur Machen. The original story was published in 1890, and Machen revised and extended it in 1894. On publication it was widely denounced by the press as degenerate and horrific because of its decadent style and sexual content. Machen’s story was only one of many at the time to focus on Pan as a useful symbol for the power of nature and paganism.

A woman in Wales has her mind destroyed by a scientist's attempt to enable her to see the god of nature Pan. Years later, a young woman named Helen Vaughan arrives on the London social scene, disturbing many young men and causing some to commit suicide; it transpires that she is the monstrous offspring of the god Pan and the daughter of the woman in the experiment.